docs: def _read_file(self, filename):
          """
          read a Python object from a cache file.
  
          Reads a pickled object from disk and returns it.
  
          :param filename: Name of the file that should be read.
          :type filename: str
          :rtype: object
          """
  
          if self.__compression:
              f = gzip.GzipFile(filename, "rb")
          else:
              f = open(filename, "rb")
          res = pickle.load(f)
          f.close()
          return res